Nowadays, semiconductor lasers are widely used as light sources for use with optical information equipment. Of these lasers, those for use with an optical disk of write-once type or overwritable type and the like are desired to output a high power and exhibit high reliability.
Deterioration or damage of the laser-light-emitting edge of a semiconductor laser is regarded as one of the factors of decreased reliability thereof. In an attempt to overcome such a problem, Japanese Unexamined Patent Publication No. 239679/1991, for example, discloses a method for restraining generation of heat in an edge portion due to Joule's heat by forming a current-noninjection region in the edge portion.
FIG. 7 generally shows a semiconductor laser of the conventional type having a current-noninjection region in the laser-light-emitting edge portion. This laser is of a self-aligned structure having the current-noninjection region formed adjacent an end of resonator waveguide. It is noted that FIG. 7a is a perspective view of the semiconductor laser, FIG. 7b is a sectional view taken along line V--V of FIG. 7a, and FIG. 7c is a sectional view taken along line VI--VI of FIG. 7a.
As shown in FIG. 7a, semiconductor laser 21 is fabricated in the following manner. On semiconductor substrate 5 such as made of n-GaAs are sequentially stacked lower clad layer 6 such as made of n-Al.sub.x Ga.sub.1-x As, active layer 7 of Al.sub.y Ga.sub.1-y As, first upper clad layer 8 of p-Al.sub.x Ga.sub.1-x As, current-blocking layer 9 of n-GaAs, and evaporation-preventive layer 10 of n-Al.sub.0.15 Ga.sub.0.85 As. The upper surface of the resulting structure is etched to form stripe cavity 13 reaching first upper clad layer 8, followed by stacking second upper clad layer 11 of p-Al.sub.x Ga.sub.1-x As and contact layer 12 of p-GaAs. Finally, second electrode 2 and first electrode 3 are respectively formed on the upper and lower surfaces of the resulting structure, namely on the upper surface of contact layer 12 and on the lower surface of semiconductor substrate 5, and the resultant is cut into chips.
The above mentioned stripe cavity 13 is defined in a central portion of the chip and surrounded by current-blocking layer 9 and evaporation-preventive layer 10 as shown in FIGS. 7b and 7c. In this structure, current will not flow in the laser-light-emitting edge portion because current-blocking layer 9 and evaporation-preventive layer 10 are partially retained in that portion as shown in FIG. 7b. Hence, the edge portion becomes a current-noninjection portion which serves to restrain generation of heat due to Joule's heat thereby making the laser-light-emitting edge hard to deteriorate or damage.
However, such a conventional semiconductor laser uses a direct transition material, such as GaAs, for the current-blocking layer formed in the laser-light-emitting edge portion and, hence, light absorption occurs in this portion. This results in a problem of unsatisfactory current-light output characteristic.